1. Field of the Invention
The present invention relates to apparatus, and methods related to guiding an axial medical instrument, such as a needle or probe, during a medical procedure.
2. Description of the Background of the Invention
During medical procedures it is often necessary for a surgeon to insert an axial surgical instrument, such as a needle, shunt, or probe, into a patient to reach a pre-selected target within the body of the patient. Some exemplary surgical procedures where this necessary include biopsy procedures and invasive neurosurgical procedures. In order to obtain relatively accurate placement of the axial surgical instrument, it is currently customary to use navigation techniques that rely on one or more images of the patient that include the target, such as well known computed tomography (CT) techniques, which provide three-dimensional volume image information of the patients body (i.e., a “CT image” or “CT data set”). As used herein, the term CT is not limited to a particular scanning technology, and encompasses any available technology, such as X-ray, 2D projection X-ray, C arm devices, magnetic resonance imaging, ultrasound, and other types of imaging devices capable of producing an image or a volume slice of the patient's body usable for planning and performing a navigated surgical procedure.
After a CT image is obtained of the patient, the target and an entry point are identified in the CT image by the medical personnel and from these points a linear trajectory for the surgical instrument is identified. This is often performed with the assistance of computer system controlled with appropriate software, which will calculate a pitch angle and a yaw angle with respect to a vertical gravity vector and a coordinate system relative to the CT scanner. The entry point is marked on the patient by known mapping techniques, such as with reference to a grid or other marker visible on both the patient and in the CT image. From the pitch and yaw angles, the trajectory may then be transferred from the image space to the actual patient space, and the surgical instrument can be aligned with respect to the entry point.
Thus, for example, in interventional radiology percutaneous needle placement under CT guidance is a state of the art procedure. The patient is positioned in a gantry of a CT scanner and several CT scans are obtained at different times during the procedure to localize the entry point and insert the needle to the target point in the body. Some exemplary applications include soft tissue biopsies (e.g. lung, liver, kidney), bone biopsies, vertebroplasty, RF ablation, etc. The procedure is typically performed with a straight needle-shape instrument. Localization of the entry point is generally less problematic than localization of the target point inside the patient. For entry point localization, the patient is typically scanned with a grid in the area of interest. The grid stripes are identified in the CT scan and are used to correlate the planned entry point as identified in the CT image with the physical entry point on the patient. For target point localization the physician usually has to align the angle manually according to the plan from the CT image and needs regular periodic scanning to monitor and control the trajectory. Thus guidance of the needle to the target is an iterative process with iterative control scans and often requires a revision of the needle trajectory path if the target is missed. This makes the procedure time consuming and yields a high amount of X-ray exposure to the patient and physician. Modern CT scanners provide a “CT-Fluoro” mode which allows constant imaging in a few slices. This feature allows the physician to visualize live the penetration of the needle into the tissue, but it also exposes the patient and staff to a high dosage of X-ray and allows only approaches in the axial plane of the CT (“in plane approach”). Often, however, an approach to the target in the plane of the CT scan is not possible, such as when a rib blocks the approach or when critical soft tissue would have to be penetrated.
Other known methods for aligning the surgical instrument in the patient space in the same orientation as planned in the CT image space are often cumbersome and/or require complex navigation systems.
Some systems use a surgical navigation system to help the surgical personnel guide a needle. For example, U.S. Patent Application Publication No. 2008/0200798, discloses a biopsy needle guide that has two independent arcuate angle guides to allow a guide tube to be pivoted about a single point and that is adapted to be adhesively attached to the skin of the patient. The needle guide is specially adapted to be visible in the CT scan image and also has specially adapted navigation markers that are tracked by a separate optical computer surgical navigation system in a manner known in the art. Images from the surgical navigation system are then registered with the CT scan images to allow the surgical staff to ensure that the needle guide is aligned on the patient in the orientation as defined in the CT scan image. In one embodiment, the biopsy needle guide is specially designed with spaced apart markers to help identify proper alignment with the CT scan image plane. Another needle guidance system based on an optical navigation system is disclosed in U.S. Pat. No. 7,876,942, in which an optical navigation camera is attached directly to a biopsy needle and a patch with fiducial markers is attached to the patient in the region of the selected entry point on the patient. Such systems, however, require complex optical surgical navigation systems in addition to CT imaging apparatus and usually require the attachment of tracking markers on the patient in order to be able to register the CT image with the patient.
In other systems, a biopsy needle is aligned in relation to the local vertical gravity vector without the use of an optical computer surgical navigation system. Some representative systems that operate on this principle are disclosed by U.S. Patent Application Publication No. 2005/0033315; EP 0 414 130; and EP 0 535 378. In these systems, generally, a bubble level or other mechanical leveling device is used to and maintain an alignment guide in a level plane, i.e., perpendicular to the local vertical gravity vector, so that a needle may be inserted at some defined trajectory angle while keeping the needle guide level. A drawback of these systems, however, is that the alignment guides must generally be maintained in the level condition and aligned in the plane of a perpendicular CT scan image plane in order to be able to accurately define the desired trajectory.
EP 1 977 704 discloses an alignment guide that uses pendulums to automatically identify the gravity vector in two, perpendicular planes so that the needle guide may be angularly adjusted in two independent, perpendicular planes. In this manner, the needle is adjusted about a yaw angle (transverse horizontal axis) by one set of pendulums, and has a protractor for adjusting the needle entry angle about the pitch angle (longitudinal horizontal axis). The alignment guide is designed to be held freehand by an operator and not to be attached to the patient. Again, a drawback of this system is that the alignment guide must be maintained at a particular level orientation in at least one degree of rotational freedom.
The inventors of the present invention have developed a system that can overcome at least some of the drawbacks of the previously known systems by eliminating the need for an external optical navigation system or the need to maintain the axial guide in particular the level plane before being able to calculate the desired trajectory in the patient space.